Arc flash detection system and method

ABSTRACT

A sensor to simultaneously detect light and acoustic waves is presented. The sensor includes one or more optical fibers and a diaphragm disposed near one end of at least one of the one or more optical fibers. The diaphragm is configured to vibrate upon incidence of acoustic waves from an arc flash and reflect a light beam into at least the one of the one or more of the optical fibers. A semi-transparent region is disposed around the one or more optical fibers to diffuse light originating from the arc flash into at least one of the one or more optical fibers.

BACKGROUND

The invention relates generally to arc flash detection and, inparticular, to arc flash sensors.

Electric power circuits and switchgear equipment have conductorsseparated by insulation. Air space often serves as part or all of thisinsulation in some applications. If the conductors are too close to eachother or voltage exceeds the insulation level, an arc can occur betweenconductors. Air or any other insulation (gas, solid, or liquid) betweenconductors can become ionized, making the insulation conductive andthereby enabling an arcing event. Arc events may induce temperaturesthat can reach as high as 20,000° C., vaporize conductors and adjacentmaterials, and release an explosive energy that destroys surroundingcircuits.

An arc flash is typically the result of a rapid energy release due to anarcing fault between two phases or between one phase and a neutral orground. An arc flash can produce high heat, intense light, and acousticwaves similar to that of an explosion. However, an arc fault currenttypically includes a much lower magnitude as compared to a short circuitcurrent, and circuit breakers do not necessarily react to such lowermagnitudes of current. Typically, arc flash mitigation techniques usestandard fuses and circuit breakers. However, such techniques have slowresponse times and are not fast enough to mitigate an arc flash.

One technique to mitigate arc faults is to reduce the response time ofarc sensors. For example, reduced response time may be achieved bydetecting specific characteristics of the arcing event such as light.Optical sensors detect light within an enclosure and determine theoccurrence of the arc flash event. However, such a method of lightdetection may lead to erroneous arc detection when stray light or lightfrom other sources is detected. Further, such methods do not provideinformation regarding the location of the arcing event. Other techniquesinclude implementing pressure sensors within the enclosure to detect arcflash induced pressure changes. Such methods, however, result in delayeddetection as pressure build-up takes a significant amount of time.

There is a need for improved arc flash prevention mechanism that has animproved response time and minimizes false alarms.

BRIEF DESCRIPTION

Briefly, a sensor to simultaneously detect light and acoustic waves ispresented. The sensor includes one or more optical fibers and adiaphragm disposed near one end of at least one of the one or moreoptical fibers. The diaphragm is configured to vibrate upon incidence ofacoustic waves from an arc flash and reflect a light beam into at leastthe one of the one or more of the optical fibers. A semi-transparentregion is disposed around the one or more optical fibers to diffuselight originating from the arc flash into at least one of the one ormore optical fibers.

In another embodiment, an arc flash detection system is presented. Thedetection system includes one or more optical fibers and a light sourcecoupled to one of the one or more optical fibers and configured togenerate a laser beam. The system further includes a sensor comprising adiaphragm disposed near one end of the one of the one or more opticalfibers and configured to vibrate upon incidence of acoustic waves froman arc flash and reflect the laser beam into at least one of the one ormore optical fibers. The sensor further includes a semi-transparentregion disposed around the one or more optical fibers to diffuse lightoriginating from the arc flash into at least one of the one or moreoptical fibers. The system includes one or more photo detectors coupledto the sensor and configured to receive a reflected laser beamindicative of acoustic waves from the arc flash and light originatingfrom the arc flash and a processor coupled to the one or more photodetectors and configured to detect an occurrence of an arc flash.

In another embodiment, a method is proposed. The method includestransmitting a light via optical fiber to a sensor and transmittinglight that includes components representative of acoustic waves andlight from the sensor for filtering and processing to detect theoccurrence of an arc flash.

In yet another embodiment, an electrical distribution system ispresented. The electrical distribution system includes an arc flashdetection system having a light source configured to generate a lightbeam. A plurality of sensors are disposed around the electricaldistribution system, each of the sensors having one or more opticalfibers and a diaphragm disposed near one end of at least one of the oneor more optical fibers, the diaphragm configured to vibrate uponincidence of acoustic waves from an arc flash and reflect a light beaminto at least one of the one or more of the optical fibers. Each of thesensors further include a semi-transparent region disposed around theone or more optical fibers to diffuse light originating from the arcflash into at least one of the one or more optical fibers. Theelectrical distribution system further includes at least one photodetector coupled to the sensors and configured to detect reflected lightbeams from the sensors and a processor coupled to the at least one photodetector and configured to generate an arc fault signal upon detectionof an arc flash within the electrical distribution system.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an arc flash sensor according to one embodiment ofthe invention;

FIG. 2 illustrates an arc flash sensor according to another embodimentof the invention;

FIG. 3 illustrates an arc flash sensor according to another embodimentof the invention;

FIG. 4 is a block diagram of an arc detection system according to oneembodiment of the invention;

FIG. 5 is a block diagram of arc detection system according to anotherembodiment of the invention;

FIG. 6 is a block diagram of another arc detection system;

FIG. 7 is a block diagram of another arc detection system;

FIG. 8 is a graph of acoustic and light signals detected from an arcflash over time according to an embodiment of the invention;

FIG. 9 illustrates an electrical distribution system implementing arcsensors according to one embodiment of the invention;

FIG. 10 illustrates several embodiments of the diaphragm implemented inarc flash sensors; and

FIG. 11 illustrates frequency response for the diaphragms in FIG. 10.

DETAILED DESCRIPTION

FIG. 1 illustrates an arc flash sensor according to an embodiment of theinvention. The sensor 10 includes a diaphragm 12 disposed near one end13 of an optical fiber 14 having a fiber core 16 and a fiber cladding18. In one embodiment, the diaphragm 12 is configured to vibrate uponincidence of sound (acoustic waves) from an arc flash and reflect lightfrom a laser beam 30 into the fiber core 16. As used herein, acousticwaves may include pressure waves as well. In one embodiment, thediaphragm comprises opaque material made of thin film and disposed in anelongated position. In another embodiment, the diaphragm comprises asemi-transparent material. The semi-transparent material may include forexample, a thin film that has been pre-strained to respond to externalair pressure dynamics and allow light transmission of about 30% to about60%. In one embodiment, to avoid saturation of photo detectors ordetector arrays, the diaphragms comprises a metalized polymericmaterial. During fabrication of the diaphragm, metalized thin filmdeposition on the polymer film may be controlled to achieve desiredthickness.

To provide protection for the diaphragm during operation while stillallowing acoustic waves to be detected, diaphragm 12 may be enclosedwithin a protective sleeve 22 and a protective screen 24 that permitsthe acoustic waves from the external environment to reach the diaphragm.A fiber holder 20 is disposed around the optical fiber 14. In oneembodiment, the fiber holder includes a semi-transparent regionconfigured to diffuse light originating from the arc flash into thefiber core 16. One or more optional holes 25 measuring about 0.5 mm toabout 2 mm in diameter may be provided to enhance the light detectionfrom arc flash. In this embodiment, arc flash generated light isdirected through the optional hole 25 towards fiber 14. In embodimentswherein the protective screen 24 and diaphragm 12 permit some amount oflight to pass, light from an arc flash may additionally be directedtowards fiber 14 through the protective screen and the diaphragm.

In an exemplary operation, the sensor 10 is configured to receiveacoustic waves 28 and light 26 from an arc flash. The sensor 10 isconfigured to obtain signals representative of acoustic wave and lightsimultaneously. Such an integrated approach of sensing acoustic wave andlight simultaneously minimizes false alarms and enables early arc flashdetection. Fiber core 16 is configured to direct laser beam 30 on thediaphragm 12. Diaphragm 12 is configured to vibrate based on theintensity and frequency of acoustic waves from the arc flash. Based onthe vibrations, a unique pattern of light is reflected from thediaphragm in the direction of beam 31. Simultaneously, light originatingfrom the arc flash is incident on the semi-transparent region 20. Thesemi-transparent region 20 is configured to diffuse light towards thefiber core 16. In one embodiment, the semi-transparent region 20 isconfigured to diffuse light is at ultraviolet wavelengths. The distancebetween one end 13 of the optical fiber and the diaphragm 12 isoptimized such that the reflected beam from the diaphragm 12 reaches thefiber core 16 without significant transmission losses.

FIG. 2 illustrates an arc flash sensor according to another embodimentof the invention. The sensor 34 illustrates a dual fiber core designcomprising two optical fibers 14, 36 having corresponding fiber cores16, 38. One end 13 of the first optical fiber 14 is disposed proximateto the diaphragm 12. In the event of arc flash, acoustic waveoriginating form the arc flash generate vibrations in the diaphragm.Reflected beam 31 captures such vibrations that are further processed todetect an arc flash. One end 40 of the second optical fiber 36 isdisposed within the semi-transparent region 20 such that optical fiber36 is configured to transmit diffused light resulting from the arcflash. In operation, there are two optical fibers 14, 36 with firstoptical fiber 14 dedicated for acoustic wave detection and the secondoptical fiber 36 for light detection. In the illustrated embodiment,fiber core 16 is configured for both directing the laser beam 30 on thediaphragm 12 and transmitting back the reflected beam 31 from thediaphragm 12 for further processing. In one embodiment, cladding 41around the end 40 of the optical fiber 36 is removed to increase lightcoupling efficiency.

FIG. 3 illustrates an arc flash sensor according to another embodimentof the invention. Sensor 44 includes three optical fibers 14, 15, 36arranged in a manner that first optical fiber 14 is configured totransmit laser beam 30 onto the diaphragm 12 and second optical fiber 15is configured to receive the reflected beam 31 from the diaphragm 12.Third optical fiber 36 as described in FIG. 2, is configured to detectlight from the arc flash.

FIG. 4 is a block diagram of an arc detection system according to anembodiment of the invention. The detection system 50 includes a sensor52 coupled to an optical fiber cable 14. A light source 56 is coupled tothe optical fiber cable 14 via an isolator 58 and a fiber splitter 60.In one embodiment, the light source 56 comprises a light-emitting diode.In another embodiment, the light source 56 comprises a laser diode thatemits light at about near infrared wavelengths. A processor 62 isconfigured to process the combined light returning from the sensor 52that includes reflected light 31 from the sensor and light diffused 64through the semi-transparent region. In one embodiment, the processor 62is coupled to the fiber splitter 60 via optical filters 66, 68 and photodetectors 70, 72 and is further configured to generate an arc faultsignal 73. The optical filters are configured to let through certainwavelength of light and to block the rest. Photo detectors 70, 72 areconfigured to generate an equivalent electrical voltage based upon theintensity and wavelength of incident light. Such electrical voltages areconvenient for further processing via the processor 62. A protectiondevice 74 may be coupled to the processor 62 in order to mitigate thearc flash. In one embodiment, the protective device includes aprotective relay configured to trip upon receiving a signal.

In an exemplary operation, the arc detection system 50 is configured todetect acoustic waves and light from an arc flash. In case of an arcflash event 48, acoustic waves 49 and light 64, among the other things,are emitted from the arc flash. Sensor 52 is configured to detect lightand acoustic waves simultaneously. Sensor 52 may include any of theembodiments described in FIGS. 1-3, for example. In one embodiment, thearc detection system 50 is adapted to implement sensor 10 having asingle optical fiber 14 as discussed in FIG. 1. Light source 56 such asa laser diode produces laser beam that is transmitted via the opticalfiber to the sensor. Isolator 58 is disposed on the transmission end ofthe light source 56 such that the reflected beam 31 from the sensor andthe light 64 from the arc flash are blocked from entering the laserlight source 56. Fiber splitter 60 is configured to transmit laser beam30 in one direction and transmit the reflected light 31 in anotherdirection. In one embodiment, the signal beam is further passed throughfiber coupler 61 and then through the optical filters 66, 68. In a morespecific example of this embodiment, the optical filter 66 comprises aband-pass filter (of about 1550 nm) configured to pass light havingwavelength for which the reflected beam is expected to be present tophoto detector 70, and the optical filter 68 comprises a low-pass filter(of about <700 nm) configured to pass light having wavelength for whichthe arc flash light is expected to be present to the photo detector 72.Processor 62 is configured to process the signals from both the photodetectors 70, 72 and generate an arc fault signal 73 in case of arcflash event 48. Protective device 74 is activated based upon the arcfault signal 73 and configured to interrupt power to mitigate the arcflash.

FIG. 5 illustrates a block diagram of arc detection system 80 accordingto another embodiment of the invention. Instead of including twoseparate couplers 60 and 62, a 1×3 fiber splitter 82 is implemented tocouple the light source 56 and the photo detectors 70, 72. Furthermore,FIG. 5 is used to illustrate that the filters of FIG. 4 are not requiredin every embodiment. In the embodiment of FIG. 5, the photo detectorsare configured to detect a particular range of wavelengths. In oneexample, photo detector 70 is configured to detect light in the range ofabout 1550 nanometer wavelength and photo detector 72 is configured todetect light in the range from about 200 nanometer to about 700nanometer wavelength.

FIG. 6 is a block diagram of arc detection system wherein at least twooptical fibers are present in a sensor, such as described with respectto FIG. 2. In operation, light is directed from light source throughisolator 58 and coupler 90 to fiber 14 to sensor 34. Optical fiber 14 isconfigured to transmit reflected beam 31 from the diaphragm (12 asreferenced in FIG. 2), and optical fiber 36 is configured to transmitlight 64 from the arc flash. In the embodiment of FIG. 6, fiber coupler90 is implemented to couple light source 56 and photo detector 70 to thesensor 34. FIG. 7 is an alternative embodiment wherein three opticalfibers 14, 15, 36 (within a sensor of the type discussed with respect toFIG. 3) may be implemented in arc detection system 92.

FIG. 8 is a graph illustrating acoustic and light signals detected froman arc flash according to an embodiment of the invention. In anexemplary embodiment, the graph 96 is obtained by measuring the acousticand light signals in a simulated system having 480 V, 100 kA setup. Thegraph 96 depicts time in milliseconds on X-axis 98 and voltage on Y-axis100. In the illustrated embodiment, the profile 102 depicts the lightcomponent of the arc flash whereas profile 104 depicts the acousticcomponent of the arc flash. Relative time delay 99 between the detectedarc flash induced light 103 and acoustic waves 106 serves as an uniquesignature. In the certain embodiments, such relative time delay is inthe order of about 0.5 ms to about 10 ms. Such a combination of profiles102, 104 that form a unique pattern for a given system may be stored forfuture comparison. Using both acoustic and light data, and theirrelative time sequence is expected to mitigate the possibility of falsealarm, and provide the location of arc flash event.

FIG. 9 illustrates an electrical distribution system implementing arcflash sensors according to an embodiment of the invention. Electricaldistribution system 110 includes a plurality of sensors 111-120 disposedaround the system and configured to detect arc flash events. The sensorsmay include any design as discussed in FIGS. 1-3. Light source 56 iscoupled to optical fiber cable 122 and a plurality of sensors 111-120.Each sensor is coupled to photo detector array 124 via fiber couplers. Aprocessor 62 is configured to generate an arc fault signal in case anarc fault is detected within the electrical distribution system. In oneembodiment, processor 62 is configured to detect a location of the arcflash within the electrical distribution system based upon the signalsfrom the plurality of sensors disposed around the distribution system.

FIG. 10 illustrates several embodiments of the diaphragm implemented inan arc flash sensor according to an embodiment of the invention. In anexemplary embodiment the diaphragm 12 (FIG. 1) includes polymer filmwith metal film deposition as indicated by the reference numeral 126. Asingle layer of thin metal film 130 (about 5 nm to about 30 nm inthickness) is deposited on one side of the polymer film 128. In anotherembodiment, reference numeral 132 illustrates at least two layers ofthin metal films 130, 134 deposited on each side of the polymer film128. In another embodiment, reference numeral 136 illustrates thedeposition of multiple layers of thin metal films 137, 138 deposited onone or both sides of the polymer film 128. The thickness of thin metalfilm or films controls the light transmission ratio and the frequencyresponses of the diaphragm with respect to acoustic waves.

FIG. 11 illustrates frequency responses for the diaphragms in FIG. 10.Graph 142 illustrates frequency measured in kHz on the Y-axis 146 andthickness measured in micrometers on X-axis 144. Profiles 148-152 areobtained from simulation. Profile 152 is an exemplary frequency responsefor a diaphragm configured to comprise a polymer film only. Profile 150illustrates an exemplary frequency response for a diaphragm comprisingthin metal film on both sides of the polymer film (132 in FIG. 10).Profile 148 illustrates an exemplary frequency response for a diaphragmcomprising multilayer thin metal film on both sides of the polymer film(136 in FIG. 10).

Advantageously, sensors as proposed in various embodiments of theinvention may utilize low cost material and simple manufacturetechniques. Further, such sensors have fast response and highsensitivity. Integrated sensors simultaneously detect radiation such aslight and dynamic acoustic wave signals. Such integrated sensors enablefast detection of arc flash events. Optical fibers implemented for arcdetection have advantages such as immunity to electromagneticinterference, reduced size and weight, distribution capability, and noadditional power requirement. As used herein, the terms “a” and “an” donot denote a limitation of quantity, but rather denote the presence ofat least one of the referenced item.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A sensor to simultaneously detect light and acoustic waves, thesensor comprising: one or more optical fibers; a diaphragm disposed nearone end of at least one of the one or more optical fibers, the diaphragmconfigured to vibrate upon incidence of acoustic waves from an arc flashand reflect a light beam into at least the one of the one or more of theoptical fibers; and a semi-transparent region disposed around the one ormore optical fibers to diffuse light originating from the arc flash intoat least one of the one or more optical fibers.
 2. The sensor of claim 1wherein the one or more optical fibers comprise at least one opticalfiber for transmitting light from a light source to the diaphragm andfor transmitting the reflected light beam from the diaphragm and the arcflash-generated light towards a detection system.
 3. The sensor of claim1 wherein the one or more optical fibers comprise a first optical fiberhaving one end near the diaphragm for transmitting light from a lightsource to the diaphragm and for transmitting the reflected light beamfrom the diaphragm towards a detection system and a second optical fiberhaving an end disposed within the semi-transparent region fortransmitting light resulting from the arc flash towards the detectionsystem.
 4. The sensor of claim 1 wherein the one or more optical fiberscomprise a first optical fiber having one end near the diaphragm fortransmitting light from a light source to the diaphragm, a secondoptical fiber having one end near the diaphragm and for transmittingreflected light beam towards a detection system, and a third opticalfiber having an end disposed within the semi-transparent region fortransmitting light resulting from the arc flash towards the detectionsystem.
 5. The sensor of claim 1, wherein the diaphragm is installed inan elongated position.
 6. The sensor of claim 1, further comprising aprotective screen attached to the protective sleeve and configured toenable acoustic waves reach the diaphragm while preventing contaminantsfrom reaching the diaphragm.
 7. The sensor of claim 1, wherein thediaphragm comprises at least one of a transparent, a semi-transparent,or an opaque material.
 8. An arc flash detection system comprising: oneor more optical fibers; a light source coupled to one of the one or moreoptical fibers and configured to generate a laser beam; a sensorcomprising: a diaphragm disposed near one end of the one of the one ormore optical fibers and configured to vibrate upon incidence of acousticwaves from an arc flash and reflect the laser beam into at least one ofthe one or more optical fibers; a semi-transparent region disposedaround the one or more optical fibers to diffuse light originating fromthe arc flash into at least one of the one or more optical fibers; oneor more photo detectors coupled to the sensor and configured to receivea reflected laser beam indicative of acoustic waves from the arc flashand light originating from the arc flash; and a processor coupled to theone or more photo detectors and configured to detect an occurrence of anarc flash.
 9. The arc flash detection system of claim 8 wherein the oneor more photo detectors comprise at least two photo detectors configuredto detect different wavelengths of light.
 10. The arc flash detectionsystem of claim 8, wherein the one or more photo detectors comprise atleast two photo detectors and further comprising filters coupled betweenthe sensor and the photo detectors.
 11. The arc flash detection systemof claim 10, wherein the filters comprise at least one of a low-passfilter and a band-pass filter.
 12. The arc flash detection system ofclaim 8, wherein the processor is configured to provide an arc faultsignal to a protection device upon a detection of the occurrence of thearc flash.
 13. A method comprising: transmitting light via an opticalfiber to a sensor; transmitting light from the sensor that includescomponents representative of acoustic waves and light for filtering andprocessing to detect an occurrence of an arc flash.
 14. The method ofclaim 13 wherein the processing comprises determining a time delaybetween detection of acoustic waves that are indicative of an arc flashand detection of light that is indicative of an arc flash.
 15. Themethod of claim 13 further comprising generating an arc fault signal tomitigate the arc flash.
 16. The method of claim 13, wherein filteringcomprises detecting light of a plurality of wavelengths.
 17. The methodof claim 13, further comprising activating a protective device upondetection of the occurrence of an arc flash.
 18. An electricaldistribution system comprising: an arc flash detection systemcomprising: a light source configured to generate a light beam; aplurality of sensors disposed around the electrical distribution system,each of the sensors comprising: one or more optical fibers; a diaphragmdisposed near one end of at least one of the one or more optical fibers,the diaphragm configured to vibrate upon incidence of acoustic wavesfrom an arc flash and reflect a light beam into at least one of the oneor more of the optical fibers; a semi-transparent region disposed aroundthe one or more optical fibers to diffuse light originating from the arcflash into at least one of the one or more optical fibers; at least onephoto detector coupled to the sensors and configured to detect reflectedlight beams from the sensors; and a processor coupled to the at leastone photo detector and configured to mitigate an arc flash and to detecta location of the arc flash within the electrical distribution system.